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Absorption Extension

When a battery bank has been discharged abnormally low, select Morningstar controllers will provide this function to keep the batteries at the Absorption voltage longer than usual during the next charging cycle. This helps reverse any negative effects of the previous abnormally low discharge.

AGM Battery

Absorbed Glass Mat (AGM) is a type of maintenance-free, valve-regulated lead acid battery (VRLA). These batteries have the electrolyte held in glass mats, as opposed to flooded around the lead plates. AGM cells generally have a higher power density than standard ‘flooded’ lead acid cells. Consult with the battery manufacturer for proper charging voltages.


A unit of electric charge, having dimensions of electric current multiplied by time, equal to the charge transferred by a steady current of one ampere flowing for one hour, or 3,600 coulombs.


The strength of a current of electricity expressed in amperes (Amps).

Ampere (Amp)

The steady electric current produced by one volt applied across a resistance of one ohm; or a flow of one coulomb per second.

Array Max Power Voltage (Vmp)

The voltage at which the solar array will produce the maximum power output. This value will vary significantly due to environmental conditions (temperature, cloud cover, time of day, etc) and system setup (panel configuration, panel angle, etc). MPPT (maximum power point tracking) controllers such as the TriStar MPPT and SunSaver MPPT with Morningstar TrakStar™ technology are able to track this shifting value to provide the maximum amount of charging power possible.

Array Open Circuit Voltage (Voc)

The voltage output of the solar array when the output is open-circuited (nothing connected to the + and – output). Also referred to as the unloaded voltage.

Battery Service Reminder

A user-specified alarm (not enabled by default) which provides a periodic reminder that battery electrolyte levels should be checked. This feature is normally only used with wet-cell batteries. A press of the pushbutton clears this reminder.

Battery Temperature Compensation

As battery temperature fluctuates, charging voltage needs to be adjusted to keep the batteries as healthy as possible. As temperatures rise, charging voltage is decreased. As temperatures fall, charging voltage is increased. All Morningstar controllers have factory default charging setpoints based on 25C. Batteries with temperatures that deviate from 25C regularly should have temperature compensated charging.

Battery Voltage Sense

Select Morningstar controllers allow for precise measurement of battery voltage using the connection labeled ‘Battery Sense’. Long wire runs or small gauge wire connecting a controller and the battery may experience a voltage drop across the line. This can lead to undercharging of the battery. A battery sense connection should be used to provide an accurate reading of actual battery voltage to the Morningstar controller.

Bulk Charge

The charging state where all available solar / hydro / wind current is delivered to the battery.

Control Coil

One bit (either 0 or 1) used to control various functions of a MODBUS® compatible Morningstar product. Each Morningstar device has a different set of control coils, each able to perform different control functions.


The nine pin serial “port” that Morningstar uses for RS-232 communications connectivity.

Device Tree

The branched structure which appears in the Edgebar (Devices tab) and lists the various devices in the workspace and their corresponding data variables.

DIP Switch Fault

When a DIP switch is changed from On to Off or vice-versa while the controller / inverter is powered, the unit will show a fault.

Diversion Controller

Diversion charge controllers are typically used when the charging source requires a constant load, such as a wind or hydroelectric generator. When the battery charges to the designated Absorption voltage, the controller begins to divert current (excess power) to a connected diversion/dump load, typically a resistor bank or heating element. The controller adjusts diversion current flow to ensure proper battery charge regulation.

Dynamic Host Configuration Protocol (DHCP)

The protocol used by many Ethernet equipped devices to automatically obtain network information and configuration settings from a DHCP server on the network. This allows devices to be added to an Internet Protocol network with little or no manual setup. Select Morningstar controllers are DHCP equipped.

Edgebar [MSView]

The white vertical bar which contains the Device Tree (Devices tab) and Log File Tree (Log File tab). Can be moved around the workspace and changed in size.

EIA-485 (RS-485)

Introduced by the Electronic Industries Alliance (EIA) in 1983, EIA-485 is an alternative to RS-232 point-to-point serial communication. It supports multiple devices on a signal bus up to 1200m(4000ft) in length and uses differential signaling, making it less susceptible to external interference. EIA-485 is primarily used in commercial and industrial applications.

Equalization Charge

A temporary boost in charging voltage in order to stir battery electrolyte, break up deposits on the lead plates, and level cell voltages. For batteries that benefit from an equalization charge, performing one once a month for 1-3 hours is usually sufficient. Consult your battery documentation for more information.

Equalize Interval

The period of time between Equalize charge cycles. Some Morningstar controllers use a fixed interval (usually 28 days). Other Morningstar controllers allow for customization of this interval (although the default is still generally 28 days). Please refer to specific product documentation for more information.

Float Cancel

When a battery bank has been discharged extremely low, select Morningstar controllers will provide this function to keep the batteries at the Absorption voltage for the entire duration of the following charging cycle. This helps reverse any negative effects of the previous abnormally low discharge. Most Morningstar products with this feature allow for customization/disabling of this function.

Float Charge

The charging stage after the battery has been fully charged. Charging voltage is reduced to prevent excess heating and/or gassing of the battery.

Float Exit

The length of time the controller will remain in Float after battery voltage has dropped below the Float Voltage setpoint. Typically, this is the result of insufficient solar charge, heavy loads on the battery, or a combination of both. Keep mind, it’s common for heavy load to draw battery voltage down below the Float voltage for brief periods of time. Depending on the type of load used, this could happen multiple times during the Float stage. However, the Float Exit timer is a cumulative timer. If the total combined time below Float voltage exceeds the Float Exit timer value, the controller will exit Float and resume the Bulk/Absorption charge stages as necessary.

Flooded Battery

These are the most common type of battery used in renewable energy systems. They are less expensive than their Sealed counterparts, but require more maintenance. During charging, water is slowly boiled off these batteries. This requires the user to periodically refill the batteries will distilled water. How often these need to be refilled will depend upon how frequently they are discharged, how deeply they are discharged, and the charging voltage used.

GFDI (Ground Fault Detector / Interrupter)

Ground fault protection is used in electrical systems to prevent current from following any unintended paths. It is critical to detect any stray current and to interrupt (break) the circuit until safe operation can be restored. A current imbalance between the conductors of a circuit indicates a ground fault. When a ground fault is detected, Morningstar’s GFPD breaks the circuit on both the positive and the negative legs and ensures interruption of the ground fault current using a safer method than other solutions on the market.

Hazardous Location (HazLoc)

Areas where fire or explosion hazards may exist.  HazLoc is categorized by Classes, Divisions, and Groups depending on the type of substances involved and the likeness of those substances to be present. Class I, Division 2, Groups A-D Hazardous Locations include places where flammable gases or vapors such as acetylene, hydrogen, butadiene, ethylene oxide, propylene oxide, acrolein, carbon monoxide, ether, hydrogen sulfide, morphline, cyclopropane, ethyl, isoprene, acetaldehyde, ethylene, gasoline, acetone, ammonia, benzene, butane, ethanol, hexane, methanol, methane, vinyl chloride, natural gas, naphtha, propane, gasoline, acetylene, hydrogen, ethylene, propane, acetone, methane are processed but are not normally present in concentrations high enough to be ignitable (but may accidentally exist).

High Voltage Disconnect / Reconnect

The HVD/HVDR function of Morningstar controllers is designed to halt charging when battery voltage rises to dangerous levels due to another charging source in the system. It also is used to disconnect voltage sensitive loads from the system. There are two types of HVD; charging disconnect and load disconnect. When the battery voltage rises above the HVD charging threshold due to another unregulated charging source in the system, charging is halted by the Morningstar controller. Charging resumes when the battery voltage drops to the safe HVDR threshold.Loads are disconnected when the battery voltage exceeds the HVD load threshold. This is in order to protect voltage sensitive loads from a high voltage input. Loads are reconnected when the battery drops to the safe HVDR threshold.


The internal timekeeper for the Morningstar controller. While powered, the controller uses the hourmeter to keep track of total runtime and to provide a relative time for various tasks. This DOES NOT function like a real time clock.

IP Ratings

The level of protection provided by a device against the intrusion of solid objects and liquids. An IP Rating usually has two numbers: The first number represents the level of protection from solid materials and the second number represents the level of protection from liquids.

Kilovolt-Amp (kVA)

A measure of the total power in a system before power losses due to inefficiencies in the system are considered. kVA = kW/Power factor, where Power Factor is electrical efficiency ranging between 0 and 1, where 1 indicates 100% efficiency and no power losses.

KiloWatt-Hour (kWh)

A unit of energy used to determine power consumption (or power production) in the system. For example, if a solar array has produced a constant 1000W (1kW) for the duration of 5 hours, the total energy production of the solar array is 5000Wh or (5kWh). Electric companies use this unit of measurement to bill their customers for energy used.

Lead Sulfation

When a battery is being discharged the lead active material on the plates will react with the sulfate from the electrolyte forming a lead sulfate on the plates. During recharge, the lead sulfate is reconverted into lead active material and the sulfate returned to the electrolyte. If a battery is left in a discharged condition or is not properly recharged on a regular basis, the lead sulfate will become hard and have a high electrical resistance. This is what is normally called a sulfated battery. The lead sulfate may become so hard that normal recharge is unable to break down the lead sulfate crystals, rendering the battery near useless.

Log File Tree [MSView]

The branched structure which appears in the Edgebar (Log File tab) and lists the open log files in the workspace and their corresponding data variables.

Low Voltage Disconnect / Reconnect

The LVD/LVDR function of Morningstar controllers is designed to protect system batteries from overdischarge and (to a lesser extent) protect sensitive system loads from low battery voltage. When the battery drops to the LVD threshold, loads connected to the controller are shut OFF to give the batteries time to recover their charge. When the battery voltage rises above the LVDR threshold, loads that were previously disconnected are turned back ON. Low Voltage Disconnect/Reconnect does not affect the controller’s charging ability; charging continues whether in the disconnected state or in the connected state.

Metal-oxide-semiconductor field-effect transistor (MOSFET)

The most widely used field-effect transistor (FET) that controls the flow of current in a semiconductor.  Morningstar uses MOSFETs in its charge controllers.

MeterBus™ Address

The unique ID assigned to each device on a Morningstar MeterBus™ network. Needed for proper network communications.


An openly published protocol that uses character serial communication lines, Ethernet, or the internet protocol suite as a transport layer to support communication to and from multiple devices connected to the same network.

MODBUS® Address

The unique ID assigned to each device on an open protocol MODBUS® network. Needed for proper network communications.

MPPT (Maximum Power Point Tracking)

Morningstar TrakStar™ technology is used to follow the maximum power voltage of the solar array as it shifts due to changing environmental conditions. This technology allows the solar array to constantly operate at its most efficient output voltage, thereby providing the maximum amount of charging power to the batteries. This method of regulation can be significantly more efficient than standard PWM type regulation.

NEC (National Electric Code®)

Also known as NFPA 70, is a United States standard for the safe installation of electrical wiring and equipment. It is part of the National Fire Codes series published by the National Fire Protection Association (NFPA). While the NEC is not itself a U.S. law, NEC use is commonly mandated by state or local law, as well as in many jurisdictions outside of the United States. The NEC codifies the requirements for safe electrical installations into a single, standardized source.

Nominal Maximum Input Power

Specific to MPPT controllers, this is the maximum solar power the controller is able to convert to usable charge power without significant losses. This is determined by the by the nominal system(battery) voltage and the charge controller’s maximum current rating.

Nominal System Voltage

This refers to the system battery voltage, typically 12V, 24V, or 48V. Select Morningstar controllers can be configured for 36V battery systems.

Passivated Emitter and Rear Cell (PERC) Technology

Modules with modified solar cells that include an extra layer within the back side of the cell to allow some of the sun’s rays to reflect back into the solar cell to generate 6-12% more energy than ordinary solar modules.


The product of Amps multiplied by Volts and measured in Watts (W).

Pulse width modulation (PWM)

An older charging technology than MPPT that switches on and off to regulate solar array power output down to acceptable levels that can be handled and supported by batteries.  Controllers using PWM charging are generally less expensive than MPPT controllers but they deliver less power and generally don’t support  60 cell modules and oversized arrays.

PWM Absorption

The charging stage where current delivered to the battery is limited. When the battery reaches the regulation voltage, PWM (pulse width modulation) will hold the battery voltage constant. As the battery becomes more fully charged, the PWM duty cycle decreases as to allow less and less charging current to the battery. This is to avoid over-heating and over-gassing of the battery.

Resistance (Ω)

The opposition offered by a body or substance to the passage through it of a steady electric current.  Resistance is measured in ohms (Ω).


Serial communication protocol/standard available on several Morningstar products. Often requires a 9-pin serial cable (DB-9) to connect to your computer. If your computer is not equipped with a 9-pin serial power, a USB-Serial adapter is required.

Sealed Battery

Lead-acid batteries which do not need to be watered and gas much less during charging cycles than their Flooded counterparts. They tend to be more expensive, but require much less maintenance than Flooded cells. The two primary types are gel cells and AGM (absorbed glass mat).

Self-Test Fault

At start-up, and periodically during operation, Morningstar products perform various tests on internal components and circuitry. In the event an issue is detected with a component or circuit, the controller will cease operation and display the appropriate LED combination alerting the user of the failure. Additional, “Self Test Fault” will be displayed on any Morningstar meters connected to the controller. This is done to protect against potential system damage due to failed components.

SMTP (Simple Mail Transfer Protocol)

Internet standard for email transmissions. Utilized by Ethernet enabled Morningstar products for sending custom configured email notifications triggered on user-defined system conditions or events.

SNMP (Simple Network Management Protocol)

A set of communication protocols or standards for managing complex networks. Ethernet enabled Morningstar products are also SNMP enabled, allowing for relatively easy integration with large commercial/industrial applications.

Status Bar [MSView]

A standard Windows® bar running the bottom length of the MSView window. Displays the status of the Caps Lock, Num Lock, and Scroll Lock keys.


Refers to the rapid computation of array output power levels across the output voltage operating range of the array. The purpose of which is to find the array operating voltage at which the maximum amount of power is produced for the current environmental conditions. Morningstar TrakStar™ technology uses advanced sweeps to quickly and accurately find the maximum power point of the solar array and keep battery charging efficiency at a maximum.

TrakStar™ Maximum Power Point Tracking

Morningstar’s advanced maximum power point tracking algorithm designed to find and maintain operation at the solar array peak power point, maximizing energy harvest. The SunSaver MPPT and TriStar MPPT controllers feature this algorithm.

Transient Surge

A sudden release of stored energy due to incidents such as nearby lightning strikes, unfiltered electronic equipment, arcing, or generators being switched ON and OFF.


Select units require calibration for Voltage, Current, and other measurements. This is performed at the factory before shipment. Units with an Uncalibrated alarm should be returned for service.

Volt (V)

The potential difference across a resistance of one ohm when one ampere is flowing through it.


Electric potential or potential difference expressed in volts.

Watts (W)

Unit of power calculated by multiplying Amps by Voltage.

Workspace [MSView]

The space in the MSView window which is populated by various displays and the Edgebar. It contains device and display configurations. You may save a customized workspace for use at another time.